In a financial self-service apparatus, for verifying sheet-type value documents (e.g., paper currencies) in a batch processing one by one, it is required to separate the stacked sheet-type value documents, and then perform identification to each separated sheet-type value document by means of image identification, thickness detection, magnetic information detection, etc., to ensure the authenticity of the sheet-type value document to be processed, wherein the thickness detection is indispensable in the whole detection. The thickness detection information can not only serve to determine authenticity of the sheet-type value document to be processed, but also serve to determine whether the sheet-type value document mechanically separated is one piece or not, i.e., whether the separated paper currency is actually double pieces, to ensure the accuracy of counting.
Currently, most of conventional thickness detection devices are based on principles of infrared detection, optical detection and eddy current detection. However, no matter which detection method is taken, there will be a problem that oscillation of the thickness detection component occurs at an instant when a front end of a banknote rushes into the thickness detection device at a certain speed, and as reflected in a detection signal, the problem results in a peak at an initial part of the output signal and causes attenuation of the oscillation of the signal, and the attenuation time is prolonged as the rushing speed of the banknote increases (the impact is intensified). As reflected in the detection result, the problem results in that the thickness of a long area at the front end of the banknote cannot be detected effectively, and the faster the banknote runs, the larger the area at the front end of the banknote is neglected, which provides an opportunity for a counterfeit banknote to evade from the detection of the banknote identification device. Aiming at this technical issue, Chinese Patent CN101790486A discloses a device for detecting the thickness of paper which includes a reference roller, a detection roller, a detection block, a retaining block, a pressing component, a fluctuation suppressing component, and a displacement detecting component. The reference roller is arranged on a fixed rotary shaft and is a reference for determining thickness; the detection roller is arranged to be in contraposition with the reference roller and in contact with the reference roller; the detection block has one end provided with the detection roller and the other end is fixed and is freely rotatable about a support shaft, and displaces by rotatio in response to the thickness of the paper between the reference roller and the detection roller; the retaining block retains at least the support shaft of the detection block; and the pressing component, i.e., a metal leaf spring fixed on the retaining block, presses a portion of the detection block to maintain the closeness between the detection roller and the reference roller, and displaces according to the displacement by rotating of the detection block when the paper passes between the reference roller and the detection roller; the fluctuation suppressing component is configured to suppress the fluctuation of the detection roller by applying push through two ends of the support shaft; and the displacement detecting component is configured to detect the amount of displacement of the first pressing component in a non-contact manner. The device for detecting the thickness of paper is provided on the support shaft with multiple detection units composed of the detection roller, the detection block, the first pressing component, and the displacement detecting component. Though the above technical solution is capable of overcoming the problem caused by the impact, however, the impact is suppressed by the method of pushing axially to increase friction force of the detection component according to the above technical solution, which is apt to cause unsmooth movement of the detection component, and even results in failure of detection because the detection component fails to reset effectively or to reset timely. Also, precision of the machine construction will directly affect the result, and the difficulties encountered in manufacturing are great.